1. Field of the Invention
This invention relates to monolithic heat-recoverable metallic couplings.
2. Summary of the Prior Art
Heat-recoverable metallic couplings and their preparation have been described in, for example, U.S. Pat. Nos. 4,035,007 (Harrison et al) and 3,805,567 (Agius-Sinerco), the disclosures of which are hereby incorporated by reference. The couplings comprise a heat-recoverable tubular member, which may recover directly onto the pipes (or other substrates) to be coupled, as in the monolithic couplings, for example as described in the above patents, or a suitable non-heat-recoverable insert may be placed between the heat-recoverable member and the substrates, as in the composite couplings, for example described in German Offenlegungschrift No. 2,448,160 and commonly assigned U.S. applications Ser. Nos. 404,723, 404,724, 608,206 and 608,209, the disclosures of which are hereby incorporated by reference. In the monolithic couplings the heat-recoverable member is preferably provided on its inner surface with at least one, and generally at least two, teeth either side of the center of the member, the teeth being in the form of radially extending rings, the separation between the innermost teeth either side of the center of the coupling being greater than the separation between adjacent teeth on each side of the coupling. The function of these teeth is to grip and/or seal to the substrates when the member is recovered, and they cause deformation of the substrates which helps to provide these desirable results. In the known monolithic couplings the center section of the inner surface is free of teeth (and indeed has often been provided with a recess such that the ends of the tubings being coupled do not touch the coupling at any point). The conventional method of preparing such monolithic couplings is to drive a tapered mandrel through the coupling while the metal is in the martensitic state.